Chimeric VEGFRs are activated by a small-molecule dimerizer and mediate downstream signalling cascades in endothelial cells

Despite much interest in vascular endothelial growth factor (VEGF) and its receptors (VEGFRs -1 and -2), VEGF-induced signalling cascades remain incompletely defined. Attempts to assign individual responses to a particular receptor have used either transfected cell lines, receptor-specific growth factors or antisense oligonucleotides. Such studies have attributed the majority of VEGF-induced responses to activation of VEGFR-2. As a consequence of poor growth factor-induced VEGFR-1 autophosphorylation however, observations from these studies may instead reflect the relative activation of the two receptors. We have generated novel chimeric VEGF receptors in which the dimerization domain of the B subunit of DNA gyrase is fused to the cytoplasmic domain of VEGFRs -1 and -2. When expressed in porcine aortic endothelial cells, both chimeric VEGFR-1 and -2 autophosphorylate in response to addition of the small-molecule dimerizing agent, coumermycin. Once activated, both receptors induce downstream signalling cascades, exemplified here by the activation of MAPK, PLC gamma and PKB/Akt. Furthermore, we demonstrate that the Y1175 residue of VEGFR-2 is essential for the activation of PLC gamma mediated by this chimeric receptor. In contrast to previous reports which show a limited ability of VEGFR-1 to mediate signalling cascades, we show that once sufficiently activated, VEGFR-1 signals in a similar manner to VEGFR-2 in endothelial cells.